This parameter controls the maximum number of spatial zones used in a calculation, only in the case where the Courant condition step is larger than the size of the slab. That is, the step size is calculated as:

where emult is defined below, and is the maximum opacity from the previous step calculation. is only calculated from energies where the optical depth to the illuminated face of the cloud is less than taumax, where taumax is defined below. The default value for nsteps is 2.

Tim Kallman 2016-02-01